Previously, the SIFT (Scale Invariant Feature Transformation) disclosed in Non Patent Literature 1 and the HOG (Histograms of Oriented Gradients) disclosed in Non Patent Literature 2 have been proposed as art for recognizing objects depicted in still images and the characteristic points thereof. By applying this art, it is easy to determine whether or not the external appearance of objects depicted in two still images are similar, even if the objects are rotated, the magnification ratio differs or the luminosity differs. In addition, by applying the aforementioned art after reversing the object image showing the depicted object, it is possible to determine that images are similar even when the mirror image of the object is depicted.
On the other hand, Particle Video is proposed in Non Patent Literatures 3 and 4 as art for tracing movement of an object in a video. By applying this art, it is possible to acquire in what position a given location on the surface of an object in the real world is depicted in each frame image included in the video, and it is possible to identify a track of movement including that depicted position. That is to say, with this art, it is possible to identify a track expressing how a given pixel in a given frame image moves with the forward or retrograde progress of time.
Furthermore, art for searching other videos similar to the video specified by the user are proposed in Patent Literature 1.